When it comes to molding compounds for electronic components, for instance, electronic components for power electronics such as, for example, electric machines which can have, for instance, a laminated core, wire windings and a connector ring, the challenge is to put forward a molding compound that has the highest possible strength, a high resistance to media and a high tolerance against heat-induced expansion and shrinkage of the individual parts of the electronic components that are to be molded, a so-called delta-alpha tolerance.
If the molding compounds are made of a thermosetting plastic having a high cross-linking density, then, even though they exhibit sufficiently high strength and media resistance, their delta-alpha tolerance is too low. Due to the shrinkage of the individual parts of the electronic component during the cooling process in conjunction with a reduction of the free volume associated with the curing of the thermosetting plastic, such molding compounds tend towards crack formation in case of a strong substrate adhesion and thin layers, and they tend towards detachment of the molding compound from the substrate and thus towards detachment of the parts of the electronic component in case of a weak substrate adhesion and thick layers. It is precisely the curing process followed by cooling that has to be seen as being critical since the metal parts of the electronic component that serve as the substrate for the molding compound contract in this process and the molding compound itself is already quite strongly cross-linked. As a result, stresses arise in the molding compound which, either immediately or during later operation of the electronic component, can lead to the above-mentioned effects such as crack formation and/or detachment of the molding compound.
It is a known procedure to finely disperse elastomer particles in the thermosetting plastic of the molding compound in order to be able to stop cracks that are being formed in the molding compound due to crack dissipation. Such molding compounds display a relatively high strength and also a certain level of toughness, especially in the case of an abrupt stress. It is a known procedure to employ, for instance, acrylonitrile butadiene rubbers (NBR) as the elastomer particles, although these become brittle at temperatures above approximately 100° C. to 130° C., thus achieving precisely the opposite of the actual toughness modification. Consequently, the use of such molding compounds is very restricted in terms of their application temperatures since the elastomer particles become brittle or decompose within the temperature range of approximately 100° C. to 130° C. Such molding compounds cannot be used in electronic components such as, for example, also electric machines, which can display relatively high operating temperatures of up to 150° C.
Before this backdrop, the objective of the present invention is to put forward a molding compound that is characterized by its high strength and resistance to media while also displaying a high delta-alpha tolerance.